Process for preparing a sheet of polymer-based foam

ABSTRACT

A continuous process for the preparation of a polymer-based foam sheet at ambient temperatures wherein the foam is produced from a reaction product capable of curing at ambient temperatures formed by the reaction of a reactant composition comprising a prepolymer, such as an isocyanate-capped polyether, and water, comprising: 
     (a) providing a continuous substrate; 
     (b) depositing said reaction product onto said substrate; 
     (c) compressing said reaction subjecting said product to at least one compression of a predetermined degree after said reaction product has creamed but prior to the time said reaction product has finally cured; and 
     (d) finally curing said reaction product.

RELATED APPLICATIONS

This is a continuation of copending application Ser. No. 07/422,954filed Oct. 18, 1989, now abandoned, which is a continuation-in-part ofU.S. patent application Ser. No. 175,036, filed Mar. 29, 1988, by RobertW. Sessions and Roy D. Carr entitled "Hydrophilic Foam Compositions."

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel process and apparatus for theproduction of foam products and, more particularly, a process andapparatus for preparing a polymer-based foam of a predeterminedthickness that is produced without the need to slice a larger foam bunto the desired thickness. The resulting foam is suitable for useoptimally as a surgical or medical dressing.

2. Background of the Invention

Historically, the treatment of wounds involved the application ofsterile dressings such as gauze and lint to the injured area, both withand without the use of an antiseptic or curative substance. Thesedressing materials, however, suffer from a disadvantage in that theyadhere to the surface being treated or leave fibers in the wound therebyprolonging the recovery period. In an attempt to circumvent thedifficulties associated with the use of these materials, recent researchand development efforts have yielded new products which are centeredaround the use of synthetic materials as wound dressings.

The processes by which these synthetic materials, such as films andsponges, are manufactured, vary according to the composition of thesynthetic material and the properties desired in the final product.Nevertheless these processes possess many similarities. Generally, eachprocess involves formulating a polymer-based foam precursor, providing asubstrate, applying this foam precursor onto the substrate, and curingthe resulting foam by applying heat. Such processes are typicallyextended by slicing a relatively thick foam bun into a final producthaving the desired thickness. However, the combination of the use ofheat to effect curing as well as slicing the resulting product to thedesired thickness increase the cost of the final product. Moreover, inthe latter case, the addition of an extra step during productionsignificantly lowers the overall efficiency of the process.

The determination of the amount of heat to effect curing of the foammaterial is further complicated by the desire to retain a certain amountof moisture in the final foam product. This moisture is preferred as itacts to enhance the appearance, texture, and wettability of the product.Thus, the use of heat to effect curing necessitates a complex analysisto determine the optimal amount of heat to use during the curing phasewhich will effect the proper curing of the foam while not resulting inthe final product having less than the desired degree of moisture.Therefore, it would be advantageous to provide a process which wouldenable a manufacturer to easily produce a polymer-based foam producthaving a predetermined degree of moisture without necessitating theperformance of a complex curing versus moisture loss analysis.

U.S. Pat. No. 4,660,553 illustrates a method for making a medicaldressing. This process comprises applying a layer of a foamable siliconeelastomer onto a substrate which is an absorbent for the composition. Ascraper blade or the like is then used to distribute a critical amountof the elastomer onto the substrate. Reinforcing material issubsequently placed into the elastomeric composition and the reinforcedfoam is allowed to finally cure. In order to effect curing, the foam maybe subjected either to ambient temperatures or to heat, the heat beingapplied to hasten or increase the degree of cure. After the foam hasfinally cured, the substrate is cut away from the foam product toproduce a flexible, reinforced elastomeric foam sheet. The manner inwhich the elastomer is applied onto the substrate is the only means bywhich the thickness of the final foam product may be controlled in thisprocess.

U.S. Pat. No. 3,959,049 discloses a process for making air permeableartificial leathers. This process comprises incorporating a catalyst,foam stabilizer, and optionally a pigment, into an isocyanate-terminatedpolyurethane prepolymer thereby forming a solvent free "paint". Afterthe "paint" is formed, it is coated onto release paper and a substrateis applied over the exposed portion of the "paint". Subsequently, thefoaming and polymerization reactions proceed in an atmosphere having adry-bulb temperature between 40° C. to 95° C. and a relative humidity ofat least 60 percent. The presence of heat and water at this stage of theprocess causes the reaction to advance. During the course of thisreaction, the assemblage is passed through rollers which compress theassemblage. After the compression is completed, Examples 1-4 show theassemblage being placed in a dryer at 130° C. for three minutes tofurther advance the foaming and polymerization reactions. The releasepaper is removed subsequent to this drying procedure.

Despite the variety of methods for the production of synthetic foams,there remains a need for a process for manufacturing a foam in which thethickness of the resulting foam may be accurately controlled. Further,this thickness should optimally be attainable without requiring a finalslicing procedure. Moreover, it would also be advantageous if theprocess were more energy efficient, with no heating of the foam beingrequired to effect the curing of the foam product.

Accordingly, it is a principal object of the present invention toprovide a method for the continuous production of a polymer-based foamin which the thickness of the resulting product may be very accuratelycontrolled.

A related object is to provide a method for the continuous production ofa polymer-based foam in which the foam is formed directly to apredetermined thickness without the need to slice the foam to thedesired thickness after curing.

Yet another object is to achieve a final product having a predeterminedmoisture level.

It is a further object of the present invention to provide a process forpreparing a polymer-based foam product which is more efficient thanprior processes wherein the application of heat to effect the curing ofthe product is not required.

An additional object is to provide an apparatus for accomplishing theaforesaid objects.

These and other objects and advantages of the present invention will beapparent from the following description of the invention.

SUMMARY OF THE INVENTION

The present invention is predicated on the discovery that a sheet ofpolymer-based foam of predetermined thickness may be produced directly,and without the need for slicing the finally cured foam. In accordancewith the present invention a foam of predetermined thickness may be madefrom the reaction product of a reactant composition capable of curing atambient temperatures which comprises (a) a prepolymer and (b) water, byproviding a continuous substrate, depositing the reaction product ontothe substrate, covering the reaction product with a cover sheet to forma composite, compressing the composite to a predetermined degree afterthe reaction product has creamed, but prior to final curing thereof toproduce a foam having the desired thickness, and finally curing thefoam. After the reaction product is deposited onto the substrate anduntil such time as the foam is finally cured, the process is conductedat ambient, or room, temperature.

In a further embodiment of the invention, there is provided an apparatussuitable for the continuous preparation of a sheet of polymer-based foamof a predetermined thickness that may be produced directly, and withoutthe need for slicing the finally cured foam, from a reaction productcomprising a reactant composition capable of curing at ambienttemperatures comprising a prepolymer and water. The apparatus comprisesmeans for reacting said reaction composition, means for providing acontinuous substrate, means for depositing said reaction product ontosaid substrate, means for covering said reaction product with a coversheet to form a composite, and means for compressing said composite to apredetermined degree after said reaction product has creamed but priorto the final curing thereof to produce a foam having the desiredthickness. After the reaction product is deposited onto said substrate,said foam is processed at ambient temperature until said foam is finallycured.

While the invention will be described in connection with the preferredembodiment, it is understood that the invention is not intended to be solimited. On the contrary, it is intended to cover all alternatives,modifications, and equivalents as may be included within the spirit andscope of the invention as defined by the appended claims. As an example,while the present invention will be described herein as primarily usefulfor the production of surgical and medical dressings, it should beappreciated that the method is useful for the production of otherpolymer-based foam products as well.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a schematic diagram of an apparatus used to form the foamsheet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention comprises a method and apparatus for theproduction of a foam sheet having a predetermined thickness. Further, itis contemplated that this sheet may be produced by curing the foam notat elevated temperatures, but at ambient temperature.

In view of the foregoing objects and requirements, it is thereforedesirable to select a foam prepolymer that is capable of curing atambient temperature. Moreover, the prepolymers chosen should also becapable of foaming in an aqueous system in the absence of a catalyst;however, they should not dissolve in the aqueous liquid. Additionally,it is highly desirable that these prepolymers cure to form a porouscellular foam matrix, this matrix enabling both the absorption ofexternal fluids and carriage of the chosen adjuvant by the resultingfoam composition. The formation of this cellular foam matrix ispreferred due to the large volume that is available not only forabsorption, but also to contain the chosen adjuvant.

Prepolymers contemplated by the present invention are preferably usedfor the production of a medical or surgical dressing, thus they mustalso be safe for use in the human body. Generally, polyurethaneprepolymers are suitable, and optimally, an isocyanate-capped prepolymeris used.

Isocyanate-capped polyether prepolymers, such as those disclosed in U.S.Pat. Nos. 3,903,23 and 4,137,200, are suitable for use in the presentinvention. Such prepolymers should preferably have a defined averageisocyanate functionality greater than 2. These prepolymers may be cappedwith aromatic isocyanates, such as, for example, toluene diisocyanate ormethylene diphenyl isocyanate, or with aliphatic isocyanates, such asisophorone diisocyanate. Specific isocyanate-capped polyetherprepolymers which have been found suitable for use in the practice ofthe present invention include prepolymers sold under the trademark HYPOL(W. R. Grace & Co., Lexington, Mass.). Examples include HYPOL FHP 2000,HYPOL FHP 2002, HYPOL FHP 3000, HYPOL FHP 4000, HYPOL FHP 5000, HYPOLX6100, and HYPOL hydrogel.

HYPOL 2000, HYPOL 2002, and HYPOL 3000 prepolymers are derived fromtoluene diisocyanate. FHP 2000 and FHP 2002 both have an equivalentweight (per NCO) of 625, an NCO content of 1.60 meq/g and a specificgravity of 1.19. The viscosity of FHP 2000 is 18,500 cps (BrookfieldLVF, #4 Spindle, 12 rpm at 25° C.) and that of FHP 2002 is 20,000. FHP3000 has an equivalent weight (per NCO) of 425, an NCO content of 2.35meq/g, a specific gravity of 1.15 and a viscosity (measured as describedabove) of 10,500. HYPOL hydrogel is likewise derived from toluenediisocyanate. It has an NCO content of 0.5-0.9 meq/g and a viscosity of10,000 to 12,000 cps at 25° C.

Another example of an isocyanate-capped prepolymer suitable for use inthe present invention is AQUAPOL prepolymer, commercially available fromFreeman Chemical Corporation. AQUAPOL prepolymers, which are derivedfrom toulene diisocyanate, have an NCO-value of 2.5 to 3.0 and areformed from the reaction of toluene diisocyanate and an organicpolyether polyol containing at least 40 percent by weight ethylene oxideadducts as described at Col. 2, lines 3-22 of U.S. Pat. No. 4,517,326.

A further example of an isocyanate-capped prepolymer suitable for use inthe present invention and which is derived from toluene diisocyanate issold under the trademark TREPOL. This prepolymer is commerciallyavailable from Twin Rivers Engineering. TREPOL prepolymers have an NCOcontent of 1.4 meq/g and a viscosity at 90° C. of 4,700 cps.

The HYPOL FHP 4000 and HYPOL FHP 5000 prepolymers are derived frommethylene diphenyl diisocyanate. FHP 4000 has an equivalent weight (perNCO) of 476, an NCO content of 2.10 meq/g, a Brookfield viscosity (LVF,#4 Spindle, 12 r.p.m. at 25° C.) of 20,000 and specific gravity of 1.17.FHP 5000 has an equivalent weight (per NCO) of 392, an NCO content of2.55 meq/g, a Brookfield viscosity (measured as for FHP 4000) of 18,000and a specific gravity of 1.17.

Another example of an isocyanate-capped prepolymer suitable is HYPOLX6100. This prepolymer is derived from isophorone diisocyanate and hasan NCO content of 1.8 meq/g and a viscosity at 25° C. of 12,000 cps.

The amount of prepolymer in the reactant composition used to prepare thehydrophilic foam composition is not particularly critical, but dependson a number of factors as will be described in greater detailhereinafter. One factor is the proportion of other components in thereactant composition. However, there should be sufficient prepolymer toform a polyurethane foam, to releasably contain an adjuvant, if desired,and to adequately contain hydrophilic agent. To that end, the ratio ofprepolymer to hydrophilic agent should be such that the reactantcomposition does not degrade or break-up into its separate constituents.Furthermore, while there should be sufficient prepolymer to provideintegrity to the foam, there should not be so much prepolymer that theresulting polyurethane composition becomes unworkable. Where the finalcomposition is to be applied to the skin, the resulting foam compositionis desirably relatively smooth and soft while exhibiting the desiredabsorbance characteristics so that it does not irritate or otherwiseharm the skin.

The concentration of prepolymer further depends on its isocyanatefunctionality and the degree of crosslinking desired in the final foamproduct. In general, the greater the isocyanate functionality, thegreater the degree of cross-linking in the cured foam product.Typically, the reactant composition will comprise from about 20% toabout 60% by weight prepolymer. Preferably the reactant composition willcomprise from about 45% to about 50% by weight of the prepolymer.Advantageously, the prepolymers may be used alone or in combination.

The reactant composition may, if desired, further include a hydrophilicagent which is incorporated into the foam composition to absorb externalliquid, such as wound exudate, and to retain such liquid in thecomposition. When applied to a wound, the hydrophilic agent is believedto work in conjunction with the foam to hold moisture at the surface ofthe wound. This allows healing agents exuded by the foam to beconcentrated and held at the wound surface. At the same time, thehydrophilic agent incorporated into the foam composition is believed toabsorb fluid from the wound to assist thickening of the blood, i.e., itserves as a hemostat. Absorption of exudate by the hydrophilic agent,and the subsequent swelling of the agent results in the removal ofinflammatory exudates and particles that would otherwise hinder tissuerepair or cause eschar formation. Necrotic debris and bacteria arelikewise removed as autolysis, i.e. chemical debridement, is stimulated.

The hydrophilic agent is preferably a highly absorbent polymer, commonlyknown as a superabsorbent polymer. One measure of polymer absorbency isits fluid uptake capability, well known by those skilled in the art.Hydrophilic agents suitable for use in the present invention includepolymers that are capable of absorbing at least fifty times their weightof water, that is, such agents have a fluid uptake of at least 50 ml/g.Hydrophilic agents having an even higher fluid uptake, such as of atleast about 100 ml/g and even higher are also acceptable, with thosehaving an uptake of at least about 150 ml/g being preferred. Suitablesuperabsorbent polymers include sodium and aluminum salts of starch,grafted copolymers of acrylates and acrylamides, and combinationsthereof, as well as polyacrylate salts. Of course, other absorbentmaterials may be used in combination with such highly absorbentpolymers, provided the fluid uptake of the overall combination used forthe hydrophilic agent is greater than 50 ml/g. When such agents areemployed, either alone or in combination, the resulting foam compositiondesirably has the ability to hold at least about three times its weightin liquid. In the preferred embodiment, the resulting foam compositionwill have the ability to tightly hold at least about three times itsweight in fluid. As used herein "tightly held" or "tightly bound" liquidmeans the relative amount of liquid retained by the sample aftercompression. More specifically, retained liquid is the unit weight ofliquid per unit weight of foam. It is determined by the formula:##EQU1## Tightly held liquid is a measure of the relative amount ofliquid retained by the sample after compression. It is determined byrolling an 8 pound roller over the sample ten times, and then, using theretained liquid formula to calculate the relative proportion of liquidthat was not squeezed out of the composition.

Hydrophilic polymers which have been found suitable for use in the foamcomposition of this invention are commercially available from GrainProcessing Corporation. These polymers include astarch-g-poly(2-propenamide-co-2-propenoic acid, mixed sodium andaluminum salt) sold under the trademark WATER LOCK A-222; a starch-graftcopolymer of polyacrylic acid and polyacrylamide having the chemicalname starch-g-poly(2-propenamide-co-2-propenoic acid, sodium salt), soldunder the trademark WATER LOCK A-100; a starchg-poly(2-propenamide-co-2-propenoic acid, sodium salt), sold under thetrademark WATER LOCK A-200. Superabsorbent polymers commerciallyavailable from Grain Processing Corporation under the trademark WATERLOCK D-212 and WATER LOCK D-242 are likewise suitable. These polymershave the chemical name starch-g-poly(2-propenamide-co-2-propenoic acid,mixed sodium and aluminum salt). The superabsorbent polymer commerciallyavailable under the trademark WATER LOCK G-400 is also suitable for usein the making of the hydrophilic foam composition of the presentinvention. This superabsorbent polymer may be chemically identified as apoly(2-propenamide-co-2-propenoic acid, sodium salt). Other superabsorbent powders suitable for use in the present invention are sold byGrain Processing Corporation under the trademark WATER LOCK B, C, and H.

Another example of a suitable superabsorbent polymer is poly-2-propenoicacid, sodium salt, sold under the trademark absorbent polymers sold byArakawa Chemical (USA) Inc. under the trademark ARASORB are alsosuitable. The preferred hydrophilic polymers are WATER LOCK A-100,A-200, A-222 and AQUA KEEP J-500. The hydrophilic polymers may be usedalone, or in combination, to achieve the desired absorptivitycharacteristics in the foam composition.

The hydrophilic agent may comprise additives in addition to thesuperabsorbent polymers, provided, as discussed above, the additives donot reduce the fluid uptake of the hydrophilic agent to below about 50ml water per gram of hydrophilic agent and the fluid uptake of the finalfoam composition is not less than about 3 times its weight. Examples ofsuch additives include methylcellulose, guar gum, pectin, karaya gum,chitosan, agar, acacia powder, carrageenan, gelatin, and combinationsthereof.

The amount of hydrophilic agent used and the type of agent, in terms ofits fluid uptake, that may be satisfactorily used to make the foamcomposition is not critical, but is, instead, dependent on the intendedapplication of the resulting foam composition. Stated another way, thegreater the quantity of external liquid to be absorbed, e.g., thegreater the amount of wound exudate, the greater the amount ofhydrophilic agent that should be employed. In the alternative, thegreater the amount of wound exudate to be absorbed, the greater thefluid uptake of the hydrophilic agent should be. For example, for anulcerated wound where there is a high volume of wound exudate, ahydrophilic agent with high uptake is desirable. In addition, it maywell be determined that the amount of hydrophilic agent may need to beincreased. On the other hand, where the foam is to be applied to a smallcut or light burn, it may be suitable to use less hydrophilic agent orto use a hydrophilic agent with a lower fluid uptake. Determination ofthe type and amount of hydrophilic agent used is well within the abilityof one skilled in the art in light of the disclosure herein.

The amount of hydrophilic agent utilized should not be so great as toundesirably reduce the strength of the foam composition or result in aloss of polymer from the foam, although some loss of hydrophilic agentmay be tolerated without adversely affecting the ability of the foam toabsorb external liquids. The amount of hydrophilic agent employed in thereactant composition will also depend on the absorbency of the materialused. As previously indicated, it is preferable that a sufficient amountof hydrophilic agent be employed so that the resulting foam compositionis capable of absorbing at least about three times its weight inexternal liquid. Typically this can be achieved by including from about5 wt. % to about 20 wt. % hydrophilic agent in the reactant composition.

The reactant composition of this invention may further include anadjuvant; preferably, a water-soluble adjuvant. The adjuvant isreleasably carried by the resulting foam composition for subsequentrelease to a chosen situs of application. Release of the adjuvant occursin the presence of an external liquid, such as wound exudate, which ispreferentially absorbed by the foam composition. Absorption of theexternal liquid causes at least a portion of the adjuvant to bereleased.

It will be appreciated by those skilled in the art that not all of theliquid adjuvant is necessarily released (or need it be) in the presenceof the external fluid. However, a sufficient amount of adjuvant must bereleased in order to achieve the desired result. To that end, it will beappreciated that the efficacy of the adjuvant is realized upon itsrelease from the foam composition to the situs of application. In thecase of a wound dressing, the situs is the wound, burn or the like,itself. Release of the adjuvant thus provides beneficial treatment tothe wound.

Prior to curing, the adjuvant serves as a plasticizer for the reactantcomposition. It extends the curing time of the composition therebyallowing it to be more thoroughly mixed and formed. Once cured, the foamcomposition is softened by the adjuvant, allowing the foam to be morepliable and more easily applied to the skin surface or other surface ofchoice. Additionally, the adjuvant may be somewhat hygroscopic lendingfurther to the hydrophilic nature of the foam composition.

Adjuvants suitable for use in the foam composition of the presentinvention are mono, di and polyhydric alcohols. Preferably the adjuvantsare water soluble so that they may be readily released from thecomposition upon contact of the foam composition with an externalliquid. For wound dressing applications, it is also desirable that theadjuvant be capable of contacting skin without adverse side effects. Tothat end, it is also preferable that the adjuvant comprise a chemicalcompound that will have the ability to open the skin pores to achieve ademulcent effect to relieve pain and/or irritation and to achieve anemollient effect to soften the skin and prevent maceration. It is alsopreferred that the adjuvant be compatible with therapeutic or otheragents which may be carried by the adjuvant for subsequent delivery tothe situs of application. Suitable adjuvants include water solublealcohols, including monols, diols and polyhydric alcohols. Examples ofmonols include ethyl alcohol and isopropyl alcohol. Exemplary ofsuitable diols are propylene glycol, polyethylene glycol, andpolypropylene glycol. Exemplary of suitable polyhydric alcohols areglycerin, 1,2,4-butanetriol, trimethylolpropane, pentaerythritol, andsorbitol. In general, the molecular weight of the alcohols should beless than about 1000. Mixtures of alcohols can likewise be used.

Glycerin is the preferred adjuvant because it has the attributes of amedicament, cosmetic, or therapeutic agent. When glycerin is used andthe hydrophilic agent is starch-based, it is believed that glycerincoats the hydrophilic agent to form a starch glycerite. When fluid isabsorbed by the foam, glycerin is released, thereby allowing thehydrophilic agent to swell as it absorbs fluid from the wound andcausing the foam to conform to the wound contour.

Various additional medicaments, cosmetics, and therapeutic agents may,if desired, be carried with the adjuvant and released with it to thedesired situs. This release thus allows the transmission of suchtherapeutic or other agents carried in the adjuvant to the area ofapplication outside the foam composition, further assisting in thebeneficial treatment of the wound.

Illustrative of therapeutic agents which may be incorporated into thefoam composition are Collasol 2400, Crotein SPA, Cromoist HYA, CroteinCAA and hydrocortisone acetate. Illustrative of cosmetic agents whichmay be incorporated into the foam composition are European CollagenComplex, Capture Complex Liposomes, Sardo® bath oil, a hand lotion soldunder the trademark Jergens®, Noxema® skin cream, Oil of Olay® BF, Keri®lotion, Vaseline® herbal and aloe lotion, Ben Gay® ointment, andRetin-A® cream.

The amount of adjuvant included in the reactant composition shouldpreferably be sufficient to impart softness and pliability to the foamcomposition and be capable of delivering a therapeutic agent or thelike, if included, to the environment of application. However, thevolume of adjuvant should not be so great as to weaken or gel thecomposition. Generally, it has been found that the amount of adjuvant inthe reactant composition should be from about 5 wt. % to about 30 wt. %of the reactant composition.

A wetting agent may be included in the reactant composition to providemore uniform wettability of the resulting foam. The wetting agent alsoaids in controlling the cell size of the foam and in the reticulation ofthe final foam. Wetting agents suitable for use include non-ionicsurfactants. Examples of materials that may be used as the wettingagent, either alone or in admixture, include block copolymers ofethylene oxide and propylene oxide sold under the trademark PLURONIC byBASF Wyandotte Corporation, ethoxylated sorbitan fatty acid esters,glycerol esters, polyglycerol esters, and silicone fluids. PLURONIC F-68and L-62 are preferred. As is known, PLURONIC F-68 aids in woundcleansing without causing tissue damage. The use of PLURONIC F-68 isespecially preferred because of its cleansing action, particularlybecause a portion of the surfactant may be released when the foamcomposition is exposed to the exudate of the wound. Generally, theamount of wetting agent should be from about 1% to about 10% by weightof the reactant composition, preferably from about 5% to about 7% byweight.

The wetting agent should not react with the foam composition or anycomponent of the foam formulation to create difficulties during foamformation or to adversely affect the desired characteristics of the foamcomposition in use or while being stored.

Water is a necessary component of the reactant composition as itspresence results in the initiation of the foaming reaction. It should beappreciated that the source of the water required for the foamingreaction is not critical. The water so required may be provided as aseparate component of the reactant composition, or, for example, it maybe provided by one of the other components of the reactant composition.By way of illustration, and not in limitation, the required water may beprovided with an aqueous-based cosmetic which may be incorporated intothe foam composition.

The type of water used is likewise not critical. However, for medicalapplications, purified water such as deionized or distilled water may beused. Saline solutions may also be used satisfactorily.

It will be appreciated that the relative proportion of prepolymer,adjuvant and hydrophilic agent, if the latter two are included in thereactant composition, can be varied over wide ranges in order to preparea hydrophilic foam composition having the desired release and exchangecharacteristics previously described, while likewise providing a foamcomposition that is aesthetically satisfactory, insofar as its oilyness,touch, appearance and general feel. In general, for use as a wounddressing, it is preferable that the foam composition be soft andgenerally smooth to the touch so that it does not irritate the skin.These characteristics may be achieved by properly balancing the relativeproportion of adjuvant, prepolymer, hydrophilic agent, wetting agent,and water.

By way of illustration, it has been found that if excess glycerin isused in the reactant composition the resulting foam composition has anextended cure time and a decreased ability to tightly hold externalliquid. Further, it may have an oily or spongy nonuniform surface. Onthe other hand, if insufficient glycerin is included in the reactantcomposition, the resulting foam composition has been found to be lessuniform, has relatively poor flow and porosity characteristics, hasrelatively poor dimensional stability, and absorbs liquid at a slowerrate.

Similarly, if the relative proportion of prepolymer to hydrophilic agentis too high or too low, the resulting product will not be satisfactory.The amount of hydrophilic agent must be sufficient to absorb theexternal liquid and to promote the release of the adjuvant. If theamount of hydrophilic agent is too low, there is insufficient absorptionof external liquid. On the other hand, if the amount of hydrophilicagent is too high, then the viscosity of the reactant composition willbe too high for appropriate mixing.

In general, in order for the foam composition to have the desired liquidrelease and exchange characteristics and to provide a foam compositionthat is soft to the touch and not oily, the weight ratio of prepolymerto hydrophilic agent will desirably be in the range of from about 20:1to about 20:10 and the ratio of prepolymer to adjuvant will desirably bein the range of from about 20:2 to about 20:30.

It will likewise be appreciated that the wetting agent employed and theamount used may effect the characteristics of the resulting foamcomposition. It is generally desired that the wetting agent be used inan amount such that the foam is substantially uniform and readilywettable.

Throughout this disclosure, and for purposes of illustration only, theinvention will be described in detail by referring to the production ofa foam product which is manufactured using an isocyanate-cappedprepolymer. However, it should be understood we do not intend to belimited to this single prepolymer or to the specific conditions andcomponents contained in the illustrative example, and any prepolymerswhich function in the same manner as the illustrative isocyanate-cappedprepolymer may be satisfactorily employed.

By way of illustrating the process and apparatus of the presentinvention, the preparation of a reaction product using the preferredcomponent composition disclosed in U.S. Ser. No. 175,036 will bediscussed. This composition comprises an isocyanate-capped prepolymer, ahydrophilic agent, water, a wetting agent, and an adjuvant.

Once the prepolymer is selected, the reaction product may be prepared bysimply mixing the reactants until they are well blended. This method ispreferred when only water and a prepolymer are used to produce thereaction product. However, when additional components are introduced, asin the illustrative example, it is preferable to separately prepare anaqueous phase or phases and an organic phase or phases, with theprepolymer being confined separately. The aqueous phase is prepared bydissolving the hydrophilic agent and wetting agent in water. Heat may berequired in order to fully dissolve or disperse the wetting agent. Anorganic phase or phases may also be prepared if there is an organiccomponent other than the hydrophilic agent. In the illustrative example,the adjuvant is the only other component other than the polymer itselfwhich will comprise the organic phase and, as such, it may be simplycontained within a reservoir tank until needed.

Although the aqueous phase may be prepared at ambient temperature, it ispreferable to maintain the temperature of the aqueous phase at fromabout 60° F. to about 120° F., particularly when a wetting agent isused. The temperature at which the aqueous phase is most advantageouslymaintained is about 100° F. This temperature is preferred due to itsadvantageous effect upon the dispersion of the components in the aqueousphase as well as its effect on the rate of the water-prepolymerreaction.

After each of the aqueous and organic phases are separately prepared,they are combined with the prepolymer and allowed to react and form thereaction product. It should be appreciated that the various blends andphases may be prepared by either a batch process or a continuousprocess.

Turning to FIG. 1 which serves to illustrate the present method andapparatus of the present invention, the adjuvant (or organic phase),prepolymer, and aqueous phase are transferred via inlet tubes 1, 2, and3 to a suitable reaction vessel 4 in which the phases and prepolymer arecombined for reaction. The reaction vessel 4 merely serves to mix thereactants sufficiently such that they will react to form the reactionproduct. The vessel 4 is preferably equipped with speed-controllablemixing paddles to blend the phases and a temperature control means forcontrolling the temperature of the reactants.

The mixing speed of the vessel 4 and its temperature are preferably setto a predetermined level as a variance in either parameter will affectthe properties of the resulting foam sheet. Generally, the predeterminedlevels are dependent on the flow rates of each component and morespecifically on the combined flow rate. For example, if the mixerrevolutions per minute (rpm) is too low, inadequate mixing of thereactants results. If the mixer rpm is too high, the heat build up dueto the high setting increases the reaction rate of the reactants,thereby effecting the subsequent processing of the reaction product. Byway of illustration, if the reaction proceeds too quickly, the reactionproduct may prematurely cure such that the thickness of the resultingproduct may not be able to be as accurately controlled by the subsequentcompression step. This phenomenon will be explained in more detailhereinafter. Premature failure of parts and excessive use of energy mayalso occur when the mixing speed is not optimized.

The temperature of the mixer is generally kept lower than thetemperature of the reactants because the reaction itself is exothermic.If the temperature is too high, the reaction will proceed at a muchhigher rate, thereby effecting subsequent processing of the foam, forthe reasons stated previously, and also shortening the cure time.Excessive temperatures can also cause an imbalance in carbon dioxidegeneration and polymerization which may result in a nonuniform product.

The mixing vessel is thus desirably operated at a mixing speed in therange of from about 100 to about 10,000 rpm, and at a temperature withinthe range of from about 60° F. to about 120° F. Optimally, the aqueousand organic phases are mixed in vessel 4 at a mixing speed ofapproximately 2500 rpm and at a temperature of about 90° F.

After the mixing process is completed, the reaction product isdischarged from vessel 4 through a nozzle 7 onto a continuously movingsubstrate 5. The method of and means for depositing the reaction productonto the substrate 5 is not critical to the process of the presentinvention so long as the reaction product develops a generally uniformthickness prior to being crushed between rollers 9 and 10.

The substrate may be driven by a conveyer belt 6 or, alternatively, thesubstrate may be drawn in a controlled tension environment such that itwill move at the same speed as a conveyor belt would if said belt wereused. The controlled tension environment is created by a winder which islocated at the end of the production line. As presently contemplated,the turning of this winder will not only wind the finished product intoa jellyroll configuration, but will also serve to pull the substratethrough the process. Thus, the force exerted by this environment shouldbe sufficient to unwind the substrate from its source and move itthrough the crushing rollers as well as any additional processingdevices that might be present. If this environment is selected, thesubstrate may either contact or not contact a non-driven conveyor.

In keeping with the present invention, the substrate 5 moves forwardrelative to the nozzle 7, at the same velocity as the conveyer 6. Theflow rate of the reaction product from the nozzle 7 and the velocity ofthe substrate 5 combined affect the thickness and width of the resultingfoam sheet. The velocity of the substrate is directly proportional tothe reaction time of the reaction product prior to compression by afirst set of compression rollers and effects the nature of the reactionproduct. For example, the slower the velocity of the substrate, thegreater the reaction time (the time between deposition and the initialcompression) and the less the width of the final product.

More particularly, the present method and apparatus contemplate that theconveyer 6 be designed so as to allow the velocity of the substrate tovary from about 0.1 to about 11 feet per minute, with the rate at whichthe reaction product is deposited onto the substrate 5 through nozzle 7being within the range from about 0.1 to about 2.0 pounds per minute. Inthe preferred embodiment of this invention where the reaction productleaves the reaction vessel at 90° F. after being mixed at 2500 rpm, thereaction product is deposited onto the substrate 5 at a rate ofapproximately 0.2 pounds per minute and the substrate 5 travels at avelocity of 5.0 feet per minute.

The composition of the substrate material 5 onto which the reactionproduct is deposited may vary considerably without materially effectingthe present process. For example, the substrate may be a porous ornon-porous paper or derivative thereof, a type of liner onto which thereaction product will be releasably adhered, a transfer adhesive, or apartially or completely adhesively coated material. However, thematerial selected must be able to withstand the subsequent processing towhich it will be subjected. It is therefore advantageous for thesubstrate to comprise an adhesive-coated plastic, such as polyurethaneor polyvinylidene chloride (saran). The saran should preferably beapproximately 1.0 mil in thickness and be laminated to an approximately5.5 mil coated paper for support. Adhesives that are suitable for usewill depend upon the end use application of the device. For example,where the device will be used for wound dressings, suitable adhesivesinclude medical grade acrylic adhesives.

The process, as contemplated, is advantageously carried out under acover or hood. The cover serves to prevent unwanted particulate matterfrom becoming entrained within the reaction product during processing.

After the reaction product is deposited onto the substrate, but beforethe reaction product is subjected to its initial compression by rollers9 and 10, a cover sheet 8 may be deposited onto the product to form acomposite. The cover sheet 8, which has previously been release coated,is thus releasably adhered to the product. Advantageously, the coversheet 8 is a release coated paper or plastic. It is preferred that apolystyrene sheet be used due to its flexibility, availability, and lowcost. The polystyrene sheet preferably has one side release coated andis approximately 5.5 mils in thickness.

The cover sheet 8 may be supplied by any type of suitable device, butpreferably the device will provide a continuous supply of cover sheetmaterial. The cover material is positioned onto the surface of thereaction product by a roller. Advantageously the roller which positionsthe cover sheet may be the same roller that applies the initialcompressive force to the reaction product.

Subsequent to, or simultaneously with, the application of the coversheet 8, the composite is subjected to a compressive force which servesto control the thickness of the resulting foam sheet product. It shouldbe appreciated that the timing of the compression is critical to thesuccess of the novel process. Specifically, the first compression shouldnot occur until the reaction product has creamed, i.e., until such timeas the reaction product begins to foam and rise.

While it is contemplated that the composite may undergo only onecompression, it is preferred that it undergo multiple compressions. Thecompressions are preferably accomplished on a continuous basis bypassing the composite through a series of compression means, which inthe preferred embodiment comprise a pair of rollers 9, 10 which define agap 16 therebetween. The compression means compress the creamed foam soas to effect a reduction in foam thickness of from about 5 to about 95percent of the foam thickness just prior to compression. Reductions ofthat magnitude may be effected for each of a plurality of compressions.It will be appreciated by those skilled in the art that the number ofcompressions, degree of compression, and the timing of the compressionsis critical to the properties of the final product. These factors willaffect the physical properties of the resulting product. Morespecifically, the density, thickness, width, and appearance of theproduct will be affected. In order to determine the number and degree ofcompressions for the particular reaction product and processingconditions employed, a measurement of the foam thickness of the reactantproduct that has been removed from the conveyor just after eachsequential compression should be taken after the foam has been allowedto rise to its fullest extent. This measurement should be compared witha measurement taken of the thickness of the foam reaction product thathas similarly been allowed to rise to its fullest extent withoutundergoing that compression. Such a comparison will allow an operator todetermine both the number of compressions and the degree of compressionneeded to attain a foam having the desired final thickness.

When the compression means comprise at least one pair of spaced apartrollers, which define a gap therebetween through which the compositewill pass, as in the illustrative embodiment, the gap between therollers should be such that the foam will be compressed in the amount offrom about 5 percent to about 95 percent, based on the thickness of thefoam reaction product as determined by measurements taken of the foam atthe times and under the conditions specified in the previous paragraph.For the calculation of the gap between the compression rollers and theplacement of the compression rollers from the nozzle, several factorshave to be considered. These include the cream and rise times of thereaction product, the percent rise of the reaction product per unit oftime, the desired final product characteristics, substrate speed, andthe like. These factors should be taken into account when changingconveyor speed, product width or thickness, product formulation, or thelike. The rollers should preferably be adjustable to within 0.001 inch.Optimally, these adjustments are made with reference to manuallyadjustable micrometers which are located on the ends of said rollers.According to the illustrative example, three sets of rollers, 9 and 10,11 and 12, and 13 and 14, are used.

In the illustrative embodiment of the invention, the initial compressionpreferably reduces the thickness of the reaction product by about 80percent, and each subsequent compression reduces the thickness by about40 percent. Compressing the composite in this manner results in asuperior final foam product that will emerge having a specific,predetermined thickness. For example, when the velocity of the substrate5 is 5.0 feet per minute, and the reaction product, which is producedfrom an isocyanate-capped polyether prepolymer, water, a hydrophilicagent, a wetting agent, and an adjuvant, is deposited at a rate of 0.2pounds per minute, it is preferred that the initial compression, whichcompresses the foam about 80 percent, occur after the reaction productbegins to cream, but no later than 2 seconds after the reaction productleaves the nozzle 7. The second and third compressions, each of whichcompresses the foam about 40 percent, should also occur within 55 and 70seconds, respectively, after the material has left the nozzle 7.

After the final compression, and after the product no longer adheres tothe cover sheet, it is preferred that the cover sheet 8 be removed andthe product finally cured. Alternatively, the cover sheet 8 may remainin contact with the reaction product until the reaction product isfinally cured, or beyond this time.

An important aspect of the present invention is the production of a foamproduct without the application of heat to effect the curing process.More specifically, from the time the reaction product leaves the nozzle7, until the time it is finally cured, the reaction product undergoesprocessing at ambient temperature. Processing foams of the typecontemplated by the present invention at ambient temperature isadvantageous in that less energy is consumed and less volatilization ofcomponents occurs.

Upon completion of the curing stage of the process, the resulting foamsheet product is at the desired predetermined thickness. No slicing ofthe foam to achieve the desired thickness is necessary. This results inenergy and labor savings to the foam sheet producer, making the presentnovel method and apparatus highly desirable when compared with otheravailable methods.

If desired, the foam sheet may subsequently be subjected to drying meanswherein the foam sheet is dried to a predetermined moisture level.Preferably the moisture level in the final foam product is 10 percent byweight. The moisture level of the foam is important in that thesoftness, texture, and wettability of the resulting product are affectedby variations in the moisture level. Further, the less moisture in thefoam, the more liquids it will absorb and the less problems there willbe with warped packaging. Advantageously, drying is carried out usinghot air impingement, with the air that is used for the dryer being firstdrawn through a particulate filter. It is preferable that drying beconducted while the foam is still on the conveyor, but after the coversheet is removed to enhance drying.

Returning to the illustrative example, the drying temperature shouldrange from about 100° F. to about 175° F. because the components of theproduct may be volatile or may undergo changes at temperatures higherthan 175° F., e.g., the product discolors. Preferably, the temperatureis maintained at 140° F.

The process further contemplates a dryer 15 which is between 2 and 20feet in length. The dryer is capable of producing a volume of drying airvarying from about 100 to 1000 cubic feet per minute (CFM). In thepreferred embodiment, the product is dried in a 20 foot dryer at atemperature of 140° F. with air being supplied at a rate of 500 CFM,such that the resulting product will have a final moisture content ofapproximately 10 percent by weight.

The resulting foam sheet product may then be rolled, sterilized, andpackaged in an air-impervious container. Alternatively, the sheet may becut into predetermined lengths or shapes for use in bandages or otherwound dressings of various sizes.

Thus, as has been shown, the present invention provides a process thatis more expeditious than those processes employed in the past formanufacturing sheets of foaming polymers. The process of the presentinvention is not only a more energy efficient process, but also one thatallows for a higher degree of quality and uniformity of product than waspreviously thought possible.

We claim as our invention:
 1. A continuous process for the preparationof a polymer-based porous cellular foam sheet of a predeterminedthickness wherein the foam is produced from a reaction product capableof curing at ambient temperature formed by the reaction of a reactantcomposition comprising a prepolymer and water, said processcomprising:(a) providing a continuously moving substrate for supportingthe foam sheet being formed; (b) depositing said reaction product ontosaid substrate at a rate and in an amount such that the thickness of thesheet formed by the reaction product, if allowed to rise to its fullestextent without undergoing compression, would be greater than saidpredetermined thickness; (c) allowing said reaction product to beginrising to form a rising foam sheet; (d) passing said rising foam sheetinto and through a compression zone; (e) compressing said rising foamsheet to a predetermined degree while maintaining the thus-compressedthickness of the rising foam sheet constant as it passes through saidcompression zone; (f) removing said rising foam sheet from saidcompression zone; (g) allowing the rising foam sheet exiting from saidcompression zone to rise to provide a porous cellular foam sheet of saidpredetermined thickness; and (h) finally curing said foam sheet.
 2. Theprocess of claim 1, wherein said prepolymer is a polyurethaneprepolymer.
 3. The process of claim 2, wherein said polyurethaneprepolymer is an isocyanate-capped polyether prepolymer.
 4. The processof claim 1, wherein said rising foam sheet is passed through a pluralityof said compression zones.
 5. The process of claim 1, wherein saidsubstrate is releasably adhered to said reaction product.
 6. The processof claim 1, wherein said substrate is adhered to said reaction product.7. The process of claim 1, wherein said substrate is selected from thegroup consisting of polyvinylidene chloride and polyurethane.
 8. Theprocess of claim 1, further comprising covering said reaction productwith a cover sheet after said deposition step to form a composite. 9.The process of claim 8, wherein said cover sheet is releasably adheredto said reaction product.
 10. The process of claim 8, wherein said coversheet is comprised of paper.
 11. The process of claim 8, wherein saidcover sheet is comprised of plastic.
 12. The process of claim 11,wherein said cover sheet is comprised of polystyrene.
 13. The process ofclaim 8, further comprising removing said cover sheet after saidreaction product is finally cured.
 14. The process of claim 1, furthercomprising drying said reaction product after said product has finallycured.
 15. The process of claim 14, wherein said drying is accomplishedby dry air impingement.
 16. The process of claim 14, wherein said dryingis conducted until said reaction product has a moisture content of about10 percent by weight.
 17. The process of claim 1, wherein said processis carried out in a particulate-free environment.
 18. The process ofclaim 1, wherein the predetermined degree of compression is in the rangeof from about 5 percent to about 95 percent of the thickness of saidfoam sheet just prior to said compression.
 19. The process of claim 1,wherein said rising foam sheet is passed through a plurality ofcompression zones and the degree of each compression is in the range offrom about 5 percent to about 95 percent of the thickness of said foamsheet just prior to said compression.
 20. The process of claim 1, saidreactant composition further comprising a hydrophilic agent capable ofabsorbing water.
 21. The process of claim 20, said reactant compositionfurther comprising an adjuvant comprising an alcohol.
 22. The process ofclaim 21, wherein said alcohol is selected from the group consisting ofwater soluble monols, diols, and polyhydric alcohols.
 23. The process ofclaim 22, further comprising a wetting agent.
 24. The process of claim23, wherein said prepolymer is selected from the group consisting ofisocyanate-capped polyether polyols having an isocyanate equivalentweight of from about 0.5 meq/g to about 2.5 meq/g and mixtures thereof.25. The process of claim 23, wherein said prepolymer is present in anamount of from about 20 wt. % to about 50 wt. % of the total reactantcomposition.
 26. The process of claim 23, wherein said prepolymer ispresent in an amount of from about 45 wt. % to about 50 wt. % of thetotal reactant composition.
 27. The process of claim 23, wherein saidhydrophilic agent is an absorptive polymer capable of absorbing waterand having a fluid uptake of at least about 50 ml of water per gram ofsaid polymer.
 28. The process of claim 23, wherein said hydrophilicagent is an absorptive polymer having a fluid uptake of at least about100 ml of water per gram of said polymer.
 29. The process of claim 23,wherein said hydrophilic agent is an absorptive polymer having a fluiduptake of at least about 150 ml of water per gram of said polymer. 30.The process of claim 23, wherein said hydrophilic agent is a memberselected from the group consisting of starch grafted copolymers ofacrylate salts, starch grafted copolymers of acrylamide salts,polyacrylate salts, and mixtures thereof.
 31. The process of claim 23,wherein said hydrophilic agent is present in an amount sufficient toprovide a foam composition capable of absorbing at least about 3 timesits weight of liquid.
 32. The process of claim 30, wherein saidhydrophilic agent is present in an amount sufficient to provide a foamcomposition capable of absorbing at least about 3 times its weight ofliquid.
 33. The process of claim 31, wherein said foam composition iscapable of tightly carrying at least about 3 times its weight of liquid.34. The process of claim 32, wherein said foam composition is capable oftightly carrying at least about 3 times its weight of liquid.
 35. Theprocess of claim 23, wherein said alcohol is a monol.
 36. The process ofclaim 23, wherein said alcohol is a diol.
 37. The process of claim 23,wherein said alcohol is a polyhydric alcohol.
 38. The process of claim37, wherein said polyhydric alcohol has a molecular weight of less thanabout
 1000. 39. The process of claim 23, wherein said alcohol is amember selected from the group consisting of isopropyl alcohol, ethanol,propylene glycol, polyethylene glycol, polypropylene glycol, glycerine,1,2,4-butanetriol, trimethylolpropane, sorbitol, pentaerythritol, andmixtures thereof.
 40. The process of claim 32, wherein said alcohol isglycerin.
 41. The process of claim 23, wherein said alcohol is presentin an amount of from about 5 wt. % to about 30 wt. % of the reactantcomposition.
 42. The process of claim 23, wherein said wetting agent isa non-ionic surfactant selected from the group consisting of blockcopolymers of ethylene oxide and propylene oxide, ethoxylated sorbitanfatty acid esters, glycerol esters, polyglycerol esters, silicone fluidsand mixtures thereof.
 43. The process of claim 42, wherein said wettingagent is present in an amount of from about 1 wt. % to about 10 wt. % ofsaid reactant composition.
 44. The process of claim 23, wherein saidprepolymer, said hydrophilic agent and said adjuvant are present in thereactant composition such that the ratio of prepolymer to hydrophilicagent is in the range of from about 20:1 to about 20:10 and the ratio ofprepolymer to adjuvant is in the range of from about 20:2 to about20:30.
 45. The process of claim 44, wherein said prepolymer is a memberselected from the group consisting of isocyanate-capped polyetherpolyols having an isocyanate equivalent weight of from about 0.5 meq/gto about 2.5 meq/g, said hydrophilic agent is a member selected from thegroup consisting of starch grafted copolymers of acrylate salts, starchgrafted copolymers of acrylamide salts, polyacrylate salts and mixturesthereof; said adjuvant is a member selected from the group consisting ofethanol, isopropyl alcohol, propylene glycol polyethylene glycol,polypropylene glycol, glycerine, 1,2,4-butanetriol, trimethylolpropane,sorbitol, pentaerythritol, and mixtures thereof; said reactantcomposition includes a wetting agent and said wetting agent is a memberselected from the group consisting of block copolymers of ethylene oxideand propylene oxide, ethoxylated sorbitan fatty acid esters, glycerolesters, polyglycerol esters, silicone fluids and mixtures thereof, andsaid water is a member selected from the group consisting of deionizedwater, distilled water and normal saline.
 46. The process of claim 45,wherein said prepolymer is an isocyanate-capped polyether prepolymerhaving an isocyanate equivalent weight of about 1.6 meq/g and anequivalent weight per isocyanate group of about 625; said hydrophilicagent is starch-g-poly(2-propenamide-co-2-propenoic acid, mixed sodiumand aluminum salt); said adjuvant comprises glycerine, and said wettingagent is a member selected from the group consisting of block copolymersof ethylene oxide and propylene oxide.
 47. A continuous process for thepreparation of a polymer-based porous cellular foam sheet of apredetermined thickness wherein the foam is produced from a reactionproduct capable of curing at ambient temperature formed by the reactionof a reactant composition comprising an isocyanate-capped polyetherprepolymer and water, said process comprising:(a) providing acontinuously moving substrate at a rate of about 0.1 to about 11 feetper minute; (b) depositing said reaction product onto said substrate ata rate of from about 0.1 to about 2.0 pounds per minute and such thatthe thickness of the sheet formed by the reaction product, if allowed torise to its fullest extent without undergoing compression, would begreater than said predetermined thickness; (c) allowing said reactionproduct to begin rising to form a rising foam sheet; (d) passing saidrising foam sheet into and through a compression zone; (e) compressingsaid rising foam sheet to compress said rising foam sheet to apredetermined degree while maintaining the thus-compressed thickness ofthe rising foam sheet constant; (f) removing said rising foam sheet fromsaid compression zone; (g) allowing the rising foam sheet exiting fromsaid compression zone to rise to provide a porous cellular foam sheet ofsaid predetermined thickness; and (h) finally curing the foam sheet. 48.The process of claim 47, wherein said continuously moving substrate isprovided at a rate of about 5 feet per minute and said reaction productis deposited onto said substrate at a rate of about 0.2 pounds perminute.
 49. The process of claim 48, wherein the temperature of saidreaction product upon deposition ranges from about 60° F. to about 120°F.
 50. The process of claim 49, wherein the temperature of said reactionproduct upon deposition is about 90° F.
 51. The process of claim 45,wherein the predetermined degree of compression is in the range of fromabout 5 percent to about 95 percent of the thickness of said foam sheetjust prior to said compression.
 52. The process of claim 45, whereinsaid rising foam sheet is passed through a plurality of compressionzones and the degree of each compression is in the range of from about 5percent to about 95 percent of the thickness of said foam sheet justprior to said compression.
 53. The process of claim 52, wherein saidrising foam sheet is passed through three compression zones with thedegree of said first of three compressions being about 80 percent of thethickness of said foam sheet just prior to the first compression, thedegree of said second compression is about 40 percent of the thicknessof said foam sheet prior to the second compression, and the degree ofsaid third compression is about 40 percent of the thickness of said foamsheet prior to the third compression.
 54. The process of claim 47,wherein said rising foam sheet is passed through three compressionzones.
 55. The process of claim 47, further comprising covering saidreaction product with a cover sheet after said deposition step to form acomposite.
 56. The process of claim 55, wherein providing said substrateis accomplished by means comprising a continuously moving conveyor belt.57. The process of claim 55, wherein providing said substrate isaccomplished by means comprising a winding device.
 58. The process ofclaim 55, further comprising removing said cover sheet after saidreaction product is finally compressed and said product no longeradheres to said cover sheet.
 59. The process of claim 47, furthercomprising drying said product after said product is finally cured at atemperature ranging from about 100° F. to about 175° F.
 60. The processof claim 59, wherein said drying is conducted at a temperature of about140° F.
 61. The process of claim 59, wherein said drying step isconducted in a particulate-free environment.